1. Field of the Invention
The present invention relates to a document reading apparatus for reading an image on a document, used as an image input device for an image processing system such as an image processing computer, a high-speed facsimile, an electronic filing system, and an intelligent copier system.
2. Description of the Prior Art
With the recent spread of digital networks, there have been proposed various types of intelligent copier systems, digital facsimiles, and electronic filing systems. For reading an image on a document in such systems, there are often required not only the entry of image information, but also the entry of image position at the same time.
A document scanning system for converting the image information on a document into electric signals and a tablet input device for entering the position information on a document are known. For example, in the document reading apparatus as shown in Nikkei Electronics, Vol. No. (Sept. 10, 1984), pages 161-194 or the image processing system as shown in Nikkei Computer, Vol. No. (Oct. 14, 1985), pages 75-91, image information is once stored in a memory device such as a semiconductor memory, and then edited on a display device such as a CRT with the use of a tablet or a mouse. In such system, however, the image on the CRT may be turned upside down due to a document placing error, or the vertical and horizontal directions of a document may not be coincident with those of the image on the CRT. As disclosed in Japanese Laid-Open Patent Application No. 57-38065 or No. 57-180269, there is also known a system in which a tablet is switchingly connected to a document reading means. However, this system has such defects that position entry cannot be made for thick books because, as already known, the tablet is useful only for a thin document due to its low effective reading height, and that a positional shift may occur because a document surface to be read is pressed after the position information has been entered. Also, systems in which a document surface to be read is placed face upward are known as a hand scanner, or as disclosed in the Japanese Laid-Open Patent Applications No. 58-43657 and No. 58-141075. In these systems, a document surface to be read is placed upward so that the placed position can be visually checked, but position entry cannot be made.